Three-dimensional memory device with straddling drain select electrode lines and method of making thereof

ABSTRACT

An alternating stack of insulating layers and spacer material layers is formed over a substrate. The spacer material layers are formed as, or are replaced with, electrically conductive layers. An insulating cap layer is formed over the alternating stack. After formation of memory stack structures through each layer of the alternating stack and the insulating cap layer, a line trench straddling a neighboring pair of rows of the memory stack is formed. Sidewalls of the line trench include a sidewall of each memory stack structure within the neighboring pair of rows of the memory stack structures. A drain select gate dielectric and a drain select electrode line are formed within the line trench. The drain select electrode line controls flow of electrical current through an upper portion of a vertical semiconductor channel within each memory stack structure below the drain regions to activate or deactivate the neighboring rows.

FIELD

The present disclosure relates generally to the field of semiconductordevices, and particular to a three-dimensional memory device employingdrain select electrode lines that straddle neighboring rows of memorystack structures and methods of manufacturing the same.

BACKGROUND

Three-dimensional vertical NAND strings having one bit per cell aredisclosed in an article by T. Endoh et al., titled “Novel Ultra HighDensity Memory With A Stacked-Surrounding Gate Transistor (S-SGT)Structured Cell”, IEDM Proc. (2001) 33-36.

SUMMARY

According to an aspect of the present disclosure, a three-dimensionalmemory device is provided, which comprises: an alternating stack ofinsulating layers and electrically conductive layers located over asubstrate; an insulating cap layer overlying the alternating stack;memory stack structures arranged in rows that laterally extend along afirst horizontal direction and extending through each layer of thealternating stack and the insulating cap layer, wherein each of thememory stack structures comprises a memory film and a verticalsemiconductor channel laterally surrounded by the memory film; a linetrench straddling a neighboring pair of rows of the memory stackstructures and extending along the first horizontal direction, whereinsidewalls of the line trench comprise a sidewall of each memory stackstructure within the neighboring pair of rows of the memory stackstructures; and a drain select electrode line located within the linetrench.

According to another aspect of the present disclosure, a method offorming a three-dimensional memory device is provided. An alternatingstack of insulating layers and spacer material layers is formed over asubstrate such that the spacer material layers are formed as, or arereplaced with, electrically conductive layers. An insulating cap layeris formed over the alternating stack. Memory stack structures extendingthrough each layer of the alternating stack and the insulating cap layerare formed, wherein each of the memory stack structures comprises amemory film and a vertical semiconductor channel laterally surrounded bythe memory film, and wherein the memory stack structure are arranged inrows that laterally extend along a first horizontal direction. A linetrench straddling a neighboring pair of rows of the memory stackstructures and extending along the first horizontal direction is formed,wherein sidewalls of the line trench comprise a sidewall of each memorystack structure within the neighboring pair of rows of the memory stackstructures. A drain select electrode line is formed within the linetrench.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic vertical cross-sectional view of an exemplarystructure after formation of at least one peripheral device, asemiconductor material layer, and a gate dielectric layer according toan embodiment of the present disclosure.

FIG. 2 is a schematic vertical cross-sectional view of the exemplarystructure after formation of an alternating stack of insulating layersand sacrificial material layers according to an embodiment of thepresent disclosure.

FIG. 3 is a schematic vertical cross-sectional view of the exemplarystructure after formation of stepped terraces and a retro-steppeddielectric material portion according to an embodiment of the presentdisclosure.

FIG. 4A is a schematic vertical cross-sectional view of the exemplarystructure after formation of memory openings and support openingsaccording to an embodiment of the present disclosure.

FIG. 4B is a top-down view of the exemplary structure of FIG. 4A. Thevertical plane A-A′ is the plane of the cross-section for FIG. 4A.

FIGS. 5A-5H are sequential schematic vertical cross-sectional views of amemory opening within the exemplary structure up to the processing stepof deposition of a second semiconductor channel layer according to anembodiment of the present disclosure.

FIG. 6A is a schematic vertical cross-sectional view of the exemplarystructure after formation of memory stack structures and support pillarstructures according to an embodiment of the present disclosure.

FIG. 6B is a top-down view of the exemplary structure of FIG. 6A. Thevertical plane A-A′ is the plane of the cross-section for FIG. 6A.

FIG. 7A is a schematic vertical cross-sectional view of the exemplarystructure after application and patterning of a photoresist layeraccording to an embodiment of the present disclosure.

FIG. 7B is a top-down view of the exemplary structure of FIG. 7A. Thevertical plane A-A′ is the plane of the cross-section for FIG. 7A.

FIG. 8A is a schematic vertical cross-sectional view of the exemplarystructure after formation of line trenches by an anisotropic etchprocess according to an embodiment of the present disclosure.

FIG. 8B is a top-down view of the exemplary structure of FIG. 8A. Thevertical plane A-A′ is the plane of the cross-section for FIG. 8A.

FIG. 8C is a magnified vertical cross-sectional view of a region of theexemplary structure of FIG. 8A.

FIG. 9A is a schematic vertical cross-sectional view of the exemplarystructure after formation of L-shaped doped regions according to anembodiment of the present disclosure.

FIG. 9B is a top-down view of the exemplary structure of FIG. 9A. Thevertical plane A-A′ is the plane of the cross-section for FIG. 9A.

FIG. 9C is a magnified vertical cross-sectional view of a region of theexemplary structure of FIG. 9A.

FIG. 10 is a schematic vertical cross-sectional view of the exemplarystructure after formation of a continuous gate dielectric layeraccording to an embodiment of the present disclosure.

FIG. 11A is a schematic vertical cross-sectional view of the exemplarystructure after formation of drain select electrode lines according toan embodiment of the present disclosure.

FIG. 11B is a top-down view of the exemplary structure of FIG. 11A. Thevertical plane A-A′ is the plane of the cross-section for FIG. 11A.

FIG. 11C is a magnified vertical cross-sectional view of a region of theexemplary structure of FIG. 11A.

FIG. 12A is a schematic vertical cross-sectional view of the exemplarystructure after formation of a contact level dielectric layer accordingto an embodiment of the present disclosure.

FIG. 12B is a magnified vertical cross-sectional view of a region of theexemplary structure of FIG. 12A.

FIG. 12C is a magnified vertical cross-sectional view of a region of analternative embodiment of the exemplary structure of FIG. 12A.

FIG. 13A is a schematic vertical cross-sectional view of the exemplarystructure after formation of a backside trench according to anembodiment of the present disclosure.

FIG. 13B is a partial see-through top-down view of the exemplarystructure of FIG. 13A. The vertical plane A-A′ is the plane of theschematic vertical cross-sectional view of FIG. 13A.

FIG. 14 is a schematic vertical cross-sectional view of the exemplarystructure after formation of backside recesses according to anembodiment of the present disclosure.

FIGS. 15A-15D are sequential vertical cross-sectional views of a regionof the exemplary structure during formation of electrically conductivelayers according to an embodiment of the present disclosure.

FIG. 16 is a schematic vertical cross-sectional view of the exemplarystructure at the processing step of FIG. 15D.

FIG. 17 is a schematic vertical cross-sectional view of the exemplarystructure after removal of a deposited conductive material from withinthe backside trench according to an embodiment of the presentdisclosure.

FIG. 18A is a schematic vertical cross-sectional view of the exemplarystructure after formation of an insulating spacer and a backside contactstructure according to an embodiment of the present disclosure.

FIG. 18B is a magnified view of a region of the exemplary structure ofFIG. 18A.

FIG. 19A is a schematic vertical cross-sectional view of the exemplarystructure after formation of additional contact via structures accordingto an embodiment of the present disclosure.

FIG. 19B is a top-down view of the exemplary structure of FIG. 19A. Thevertical plane A-A′ is the plane of the schematic verticalcross-sectional view of FIG. 19A.

DETAILED DESCRIPTION

As discussed above, the present disclosure is directed to athree-dimensional memory device employing drain select electrode linesthat straddle neighboring rows of memory stack structures and methods ofmanufacturing the same, the various aspects of which are describedbelow. The embodiments of the disclosure can be employed to form variousstructures including a multilevel memory structure, non-limitingexamples of which include semiconductor devices such asthree-dimensional monolithic memory array devices comprising a pluralityof NAND memory strings.

The drawings are not drawn to scale. Multiple instances of an elementmay be duplicated where a single instance of the element is illustrated,unless absence of duplication of elements is expressly described orclearly indicated otherwise. Ordinals such as “first,” “second,” and“third” are employed merely to identify similar elements, and differentordinals may be employed across the specification and the claims of theinstant disclosure. The same reference numerals refer to the sameelement or similar element. Unless otherwise indicated, elements havingthe same reference numerals are presumed to have the same composition.As used herein, a first element located “on” a second element can belocated on the exterior side of a surface of the second element or onthe interior side of the second element. As used herein, a first elementis located “directly on” a second element if there exist a physicalcontact between a surface of the first element and a surface of thesecond element.

As used herein, a “layer” refers to a material portion including aregion having a thickness. A layer may extend over the entirety of anunderlying or overlying structure, or may have an extent less than theextent of an underlying or overlying structure. Further, a layer may bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer may be located between any pair of horizontal planesbetween, or at, a top surface and a bottom surface of the continuousstructure. A layer may extend horizontally, vertically, and/or along atapered surface. A substrate may be a layer, may include one or morelayers therein, or may have one or more layer thereupon, thereabove,and/or therebelow.

A monolithic three-dimensional memory array is one in which multiplememory levels are formed above a single substrate, such as asemiconductor wafer, with no intervening substrates. The term“monolithic” means that layers of each level of the array are directlydeposited on the layers of each underlying level of the array. Incontrast, two dimensional arrays may be formed separately and thenpackaged together to form a non-monolithic memory device. For example,non-monolithic stacked memories have been constructed by forming memorylevels on separate substrates and vertically stacking the memory levels,as described in U.S. Pat. No. 5,915,167 titled “Three-dimensionalStructure Memory.” The substrates may be thinned or removed from thememory levels before bonding, but as the memory levels are initiallyformed over separate substrates, such memories are not true monolithicthree-dimensional memory arrays. The various three-dimensional memorydevices of the present disclosure include a monolithic three-dimensionalNAND string memory device, and can be fabricated employing the variousembodiments described herein.

Generally, a semiconductor die, or a semiconductor package, can includebe a single memory chip. Each semiconductor package contains one or moredies (for example one, two, or four). The die is the smallest unit thatcan independently execute commands or report status. Each die containsone or more planes (typically one or two). Identical, concurrentoperations can take place on each plane, although with somerestrictions. Each plane contains a number of blocks, which are thesmallest unit that can be erased by in a single erase operation. Eachblock contains a number of pages, which are the smallest unit that canbe programmed, i.e., a smallest unit on which a read operation can beperformed.

Referring to FIG. 1, an exemplary structure according to an embodimentof the present disclosure is illustrated, which can be employed, forexample, to fabricate a device structure containing vertical NAND memorydevices. The exemplary structure includes a substrate (9, 10), which canbe a semiconductor substrate. The substrate can include a substratesemiconductor layer 9 and an optional semiconductor material layer 10.The substrate semiconductor layer 9 maybe a semiconductor wafer or asemiconductor material layer, and can include at least one elementalsemiconductor material (e.g., single crystal silicon wafer or layer), atleast one III-V compound semiconductor material, at least one II-VIcompound semiconductor material, at least one organic semiconductormaterial, or other semiconductor materials known in the art. Thesubstrate can have a major surface 7, which can be, for example, atopmost surface of the substrate semiconductor layer 9. The majorsurface 7 can be a semiconductor surface. In one embodiment, the majorsurface 7 can be a single crystalline semiconductor surface, such as asingle crystalline semiconductor surface.

As used herein, a “semiconducting material” refers to a material havingelectrical conductivity in the range from 1.0×10⁻⁶ S/cm to 1.0×10⁵ S/cm.As used herein, a “semiconductor material” refers to a material havingelectrical conductivity in the range from 1.0×10⁻⁶ S/cm to 1.0×10⁵ S/cmin the absence of electrical dopants therein, and is capable ofproducing a doped material having electrical conductivity in a rangefrom 1.0 S/cm to 1.0×10⁵ S/cm upon suitable doping with an electricaldopant. As used herein, an “electrical dopant” refers to a p-type dopantthat adds a hole to a valence band within a band structure, or an n-typedopant that adds an electron to a conduction band within a bandstructure. As used herein, a “conductive material” refers to a materialhaving electrical conductivity greater than 1.0×10⁵ S/cm. As usedherein, an “insulator material” or a “dielectric material” refers to amaterial having electrical conductivity less than 1.0×10⁻⁶ S/cm. As usedherein, a “heavily doped semiconductor material” refers to asemiconductor material that is doped with electrical dopant at asufficiently high atomic concentration to become a conductive material,i.e., to have electrical conductivity greater than 1.0×10⁵ S/cm. A“doped semiconductor material” may be a heavily doped semiconductormaterial, or may be a semiconductor material that includes electricaldopants (i.e., p-type dopants and/or n-type dopants) at a concentrationthat provides electrical conductivity in the range from 1.0×10⁻⁶ S/cm to1.0×10⁵ S/cm. An “intrinsic semiconductor material” refers to asemiconductor material that is not doped with electrical dopants. Thus,a semiconductor material may be semiconducting or conductive, and may bean intrinsic semiconductor material or a doped semiconductor material. Adoped semiconductor material can be semiconducting or conductivedepending on the atomic concentration of electrical dopants therein. Asused herein, a “metallic material” refers to a conductive materialincluding at least one metallic element therein. All measurements forelectrical conductivities are made at the standard condition.

At least one semiconductor device 700 for a peripheral circuitry can beformed on a portion of the substrate semiconductor layer 9. The at leastone semiconductor device can include, for example, field effecttransistors. For example, at least one shallow trench isolationstructure 120 can be formed by etching portions of the substratesemiconductor layer 9 and depositing a dielectric material therein. Agate dielectric layer, at least one gate conductor layer, and a gate capdielectric layer can be formed over the substrate semiconductor layer 9,and can be subsequently patterned to form at least one gate structure(150, 152, 154, 158), each of which can include a gate dielectric 150, agate electrode (152, 154), and a gate cap dielectric 158. The gateelectrode (152, 154) may include a stack of a first gate electrodeportion 152 and a second gate electrode portion 154. At least one gatespacer 156 can be formed around the at least one gate structure (150,152, 154, 158) by depositing and anisotropically etching a dielectricliner. Active regions 130 can be formed in upper portions of thesubstrate semiconductor layer 9, for example, by introducing electricaldopants employing the at least one gate structure (150, 152, 154, 158)as masking structures. Additional masks may be employed as needed. Theactive region 130 can include source regions and drain regions of fieldeffect transistors. A first dielectric liner 161 and a second dielectricliner 162 can be optionally formed. Each of the first and seconddielectric liners (161, 162) can comprise a silicon oxide layer, asilicon nitride layer, and/or a dielectric metal oxide layer. As usedherein, silicon oxide includes silicon dioxide as well asnon-stoichiometric silicon oxides having more or less than two oxygenatoms for each silicon atoms. Silicon dioxide is preferred. In anillustrative example, the first dielectric liner 161 can be a siliconoxide layer, and the second dielectric liner 162 can be a siliconnitride layer. The least one semiconductor device for the peripheralcircuitry can contain a driver circuit for memory devices to besubsequently formed, which can include at least one NAND device.

A dielectric material such as silicon oxide can be deposited over the atleast one semiconductor device, and can be subsequently planarized toform a planarization dielectric layer 170. In one embodiment theplanarized top surface of the planarization dielectric layer 170 can becoplanar with a top surface of the dielectric liners (161, 162).Subsequently, the planarization dielectric layer 170 and the dielectricliners (161, 162) can be removed from an area to physically expose a topsurface of the substrate semiconductor layer 9. As used herein, asurface is “physically exposed” if the surface is in physical contactwith vacuum, or a gas phase material (such as air).

The optional semiconductor material layer 10, if present, can be formedon the top surface of the substrate semiconductor layer 9 prior to, orafter, formation of the at least one semiconductor device 700 bydeposition of a single crystalline semiconductor material, for example,by selective epitaxy. The deposited semiconductor material can be thesame as, or can be different from, the semiconductor material of thesubstrate semiconductor layer 9. The deposited semiconductor materialcan be any material that can be employed for the semiconductor substratelayer 9 as described above. The single crystalline semiconductormaterial of the semiconductor material layer 10 can be in epitaxialalignment with the single crystalline structure of the substratesemiconductor layer 9. Portions of the deposited semiconductor materiallocated above the top surface of the planarization dielectric layer 170can be removed, for example, by chemical mechanical planarization (CMP).In this case, the semiconductor material layer 10 can have a top surfacethat is coplanar with the top surface of the planarization dielectriclayer 170.

The region (i.e., area) of the at least one semiconductor device 700 isherein referred to as a peripheral device region 200. The region inwhich a memory array is subsequently formed is herein referred to as amemory array region 100. A contact region 300 for subsequently formingstepped terraces of electrically conductive layers can be providedbetween the memory array region 100 and the peripheral device region200. Optionally, a gate dielectric layer 12 can be formed above thesemiconductor material layer 10 and the planarization dielectric layer170. The gate dielectric layer 12 can be, for example, silicon oxidelayer. The thickness of the gate dielectric layer 12 can be in a rangefrom 3 nm to 30 nm, although lesser and greater thicknesses can also beemployed.

Referring to FIG. 2, a stack of an alternating plurality of firstmaterial layers (which can be insulating layers 32) and second materiallayers (which can be sacrificial material layer 42) is formed over thetop surface of the substrate, which can be, for example, on the topsurface of the gate dielectric layer 12. As used herein, a “materiallayer” refers to a layer including a material throughout the entiretythereof. As used herein, an alternating plurality of first elements andsecond elements refers to a structure in which instances of the firstelements and instances of the second elements alternate. Each instanceof the first elements that is not an end element of the alternatingplurality is adjoined by two instances of the second elements on bothsides, and each instance of the second elements that is not an endelement of the alternating plurality is adjoined by two instances of thefirst elements on both ends. The first elements may have the samethickness thereamongst, or may have different thicknesses. The secondelements may have the same thickness thereamongst, or may have differentthicknesses. The alternating plurality of first material layers andsecond material layers may begin with an instance of the first materiallayers or with an instance of the second material layers, and may endwith an instance of the first material layers or with an instance of thesecond material layers. In one embodiment, an instance of the firstelements and an instance of the second elements may form a unit that isrepeated with periodicity within the alternating plurality.

Each first material layer includes a first material, and each secondmaterial layer includes a second material that is different from thefirst material. In one embodiment, each first material layer can be aninsulating layer 32, and each second material layer can be a sacrificialmaterial layer. In this case, the stack can include an alternatingplurality of insulating layers 32 and sacrificial material layers 42,and constitutes a prototype stack of alternating layers comprisinginsulating layers 32 and sacrificial material layers 42. As used herein,a “prototype” structure or an “in-process” structure refers to atransient structure that is subsequently modified in the shape orcomposition of at least one component therein.

The stack of the alternating plurality is herein referred to as analternating stack (32, 42). In one embodiment, the alternating stack(32, 42) can include insulating layers 32 composed of the firstmaterial, and sacrificial material layers 42 composed of a secondmaterial different from that of insulating layers 32. The first materialof the insulating layers 32 can be at least one insulating material. Assuch, each insulating layer 32 can be an insulating material layer.Insulating materials that can be employed for the insulating layers 32include, but are not limited to, silicon oxide (including doped orundoped silicate glass), silicon nitride, silicon oxynitride,organosilicate glass (OSG), spin-on dielectric materials, dielectricmetal oxides that are commonly known as high dielectric constant(high-k) dielectric oxides (e.g., aluminum oxide, hafnium oxide, etc.)and silicates thereof, dielectric metal oxynitrides and silicatesthereof, and organic insulating materials. In one embodiment, the firstmaterial of the insulating layers 32 can be silicon oxide.

The second material of the sacrificial material layers 42 is asacrificial material that can be removed selective to the first materialof the insulating layers 32. As used herein, a removal of a firstmaterial is “selective to” a second material if the removal processremoves the first material at a rate that is at least twice the rate ofremoval of the second material. The ratio of the rate of removal of thefirst material to the rate of removal of the second material is hereinreferred to as a “selectivity” of the removal process for the firstmaterial with respect to the second material.

The sacrificial material layers 42 may comprise an insulating material,a semiconductor material, or a conductive material. The second materialof the sacrificial material layers 42 can be subsequently replaced withelectrically conductive electrodes which can function, for example, ascontrol gate electrodes of a vertical NAND device. Non-limiting examplesof the second material include silicon nitride, an amorphoussemiconductor material (such as amorphous silicon), and apolycrystalline semiconductor material (such as polysilicon). In oneembodiment, the sacrificial material layers 42 can be spacer materiallayers that comprise silicon nitride or a semiconductor materialincluding at least one of silicon and germanium.

In one embodiment, the insulating layers 32 can include silicon oxide,and sacrificial material layers can include silicon nitride sacrificialmaterial layers. The first material of the insulating layers 32 can bedeposited, for example, by chemical vapor deposition (CVD). For example,if silicon oxide is employed for the insulating layers 32, tetraethylorthosilicate (TEOS) can be employed as the precursor material for theCVD process. The second material of the sacrificial material layers 42can be formed, for example, CVD or atomic layer deposition (ALD).

The sacrificial material layers 42 can be suitably patterned so thatconductive material portions to be subsequently formed by replacement ofthe sacrificial material layers 42 can function as electricallyconductive electrodes, such as the control gate electrodes of themonolithic three-dimensional NAND string memory devices to besubsequently formed. The sacrificial material layers 42 may comprise aportion having a strip shape extending substantially parallel to themajor surface 7 of the substrate.

The thicknesses of the insulating layers 32 and the sacrificial materiallayers 42 can be in a range from 20 nm to 50 nm, although lesser andgreater thicknesses can be employed for each insulating layer 32 and foreach sacrificial material layer 42. The number of repetitions of thepairs of an insulating layer 32 and a sacrificial material layer (e.g.,a control gate electrode or a sacrificial material layer) 42 can be in arange from 2 to 1,024, and typically from 8 to 256, although a greaternumber of repetitions can also be employed. The top and bottom gateelectrodes in the stack may function as the select gate electrodes. Inone embodiment, each sacrificial material layer 42 in the alternatingstack (32, 42) can have a uniform thickness that is substantiallyinvariant within each respective sacrificial material layer 42.

While the present disclosure is described employing an embodiment inwhich the spacer material layers are sacrificial material layers 42 thatare subsequently replaced with electrically conductive layers,embodiments are expressly contemplated herein in which the sacrificialmaterial layers are formed as electrically conductive layers. In thiscase, steps for replacing the spacer material layers with electricallyconductive layers can be omitted.

Optionally, an insulating cap layer 70 can be formed over thealternating stack (32, 42). The insulating cap layer 70 includes adielectric material that is different from the material of thesacrificial material layers 42. In one embodiment, the insulating caplayer 70 can include a dielectric material that can be employed for theinsulating layers 32 as described above. The insulating cap layer 70 canhave a greater thickness than each of the insulating layers 32. Forexample, the thickness of the insulating cap layer 70 can be in a rangefrom twice the thickness of a spacer material layer and eight times thethickness of a spacer material layer. The insulating cap layer 70 can bedeposited, for example, by chemical vapor deposition. In one embodiment,the insulating cap layer 70 can be a silicon oxide layer.

Referring to FIG. 3, a stepped cavity can be formed within the contactregion 300 which is located between the device region 100 and theperipheral region 200 containing the at least one semiconductor devicefor the peripheral circuitry. The stepped cavity can have variousstepped surfaces such that the horizontal cross-sectional shape of thestepped cavity changes in steps as a function of the vertical distancefrom the top surface of the substrate (9, 10). In one embodiment, thestepped cavity can be formed by repetitively performing a set ofprocessing steps. The set of processing steps can include, for example,an etch process of a first type that vertically increases the depth of acavity by one or more levels, and an etch process of a second type thatlaterally expands the area to be vertically etched in a subsequent etchprocess of the first type. As used herein, a “level” of a structureincluding alternating plurality is defined as the relative position of apair of a first material layer and a second material layer within thestructure.

After formation of the stepped cavity, a peripheral portion of thealternating stack (32, 42) can have stepped surfaces after formation ofthe stepped cavity. As used herein, “stepped surfaces” refer to a set ofsurfaces that include at least two horizontal surfaces and at least twovertical surfaces such that each horizontal surface is adjoined to afirst vertical surface that extends upward from a first edge of thehorizontal surface, and is adjoined to a second vertical surface thatextends downward from a second edge of the horizontal surface. A“stepped cavity” refers to a cavity having stepped surfaces.

A terrace region is formed by patterning the alternating stack (32, 42).Each sacrificial material layer 42 other than a topmost sacrificialmaterial layer 42 within the alternating stack (32, 42) laterallyextends farther than any overlying sacrificial material layer 42 withinthe alternating stack (32, 42). The terrace region includes steppedsurfaces of the alternating stack (32, 42) that continuously extend froma bottommost layer within the alternating stack (32, 42) to a topmostlayer within the alternating stack (32, 42).

A retro-stepped dielectric material portion 65 (i.e., an insulating fillmaterial portion) can be formed in the stepped cavity by deposition of adielectric material therein. For example, a dielectric material such assilicon oxide can be deposited in the stepped cavity. Excess portions ofthe deposited dielectric material can be removed from above the topsurface of the insulating cap layer 70, for example, by chemicalmechanical planarization (CMP). The remaining portion of the depositeddielectric material filling the stepped cavity constitutes theretro-stepped dielectric material portion 65. As used herein, a“retro-stepped” element refers to an element that has stepped surfacesand a horizontal cross-sectional area that increases monotonically as afunction of a vertical distance from a top surface of a substrate onwhich the element is present. If silicon oxide is employed for theretro-stepped dielectric material portion 65, the silicon oxide of theretro-stepped dielectric material portion 65 may, or may not, be dopedwith dopants such as B, P, and/or F.

Referring to FIGS. 4A and 4B, a lithographic material stack (not shown)including at least a photoresist layer can be formed over the insulatingcap layer 70 and the retro-stepped dielectric material portion 65, andcan be lithographically patterned to form openings therein. The openingsinclude a first set of openings formed over the memory array region 100and a second set of openings formed over the contact region 300. Thepattern in the lithographic material stack can be transferred throughthe insulating cap layer 70 or the retro-stepped dielectric materialportion 65, and through the alternating stack (32, 42) by at least oneanisotropic etch that employs the patterned lithographic material stackas an etch mask. Portions of the alternating stack (32, 42) underlyingthe openings in the patterned lithographic material stack are etched toform memory openings 49 and support openings 19. As used herein, a“memory opening” refers to a structure in which memory elements, such asa memory stack structure, is subsequently formed. As used herein, a“support opening” refers to a structure in which a support structure(such as a support pillar structure) that mechanically supports otherelements is subsequently formed. The memory openings 49 are formedthrough the insulating cap layer 70 and the entirety of the alternatingstack (32, 42) in the memory array region 100. The support openings 19are formed through the retro-stepped dielectric material portion 65 andthe portion of the alternating stack (32, 42) that underlie the steppedsurfaces in the contact region 300.

The memory openings 49 extend through the entirety of the alternatingstack (32, 42). The support openings 19 extend through a subset oflayers within the alternating stack (32, 42). The chemistry of theanisotropic etch process employed to etch through the materials of thealternating stack (32, 42) can alternate to optimize etching of thefirst and second materials in the alternating stack (32, 42). Theanisotropic etch can be, for example, a series of reactive ion etches.The sidewalls of the memory openings 49 and the support openings 19 canbe substantially vertical, or can be tapered. The patterned lithographicmaterial stack can be subsequently removed, for example, by ashing.

The memory openings 49 and the support openings 19 can be formed throughthe gate dielectric layer 12 so that the memory openings 49 and thesupport openings 19 extend from the top surface of the alternating stack(32, 42) to at least the horizontal plane including the topmost surfaceof the semiconductor material layer 10. In one embodiment, an overetchinto the semiconductor material layer 10 may be optionally performedafter the top surface of the semiconductor material layer 10 isphysically exposed at a bottom of each memory opening 49 and eachsupport opening 19. The overetch may be performed prior to, or after,removal of the lithographic material stack. In other words, the recessedsurfaces of the semiconductor material layer 10 may be vertically offsetfrom the un-recessed top surfaces of the semiconductor material layer 10by a recess depth. The recess depth can be, for example, in a range from1 nm to 50 nm, although lesser and greater recess depths can also beemployed. The overetch is optional, and may be omitted. If the overetchis not performed, the bottom surfaces of the memory openings 49 and thesupport openings 19 can be coplanar with the topmost surface of thesemiconductor material layer 10.

Each of the memory openings 49 and the support openings 19 may include asidewall (or a plurality of sidewalls) that extends substantiallyperpendicular to the topmost surface of the substrate. A two-dimensionalarray of memory openings 49 can be formed in the memory array region100. A two-dimensional array of support openings 19 can be formed in thecontact region 300. The substrate semiconductor layer 9 and thesemiconductor material layer 10 collectively constitutes a substrate (9,10), which can be a semiconductor substrate. Alternatively, thesemiconductor material layer 10 may be omitted, and the memory openings49 and the support openings 19 can be extend to a top surface of thesubstrate semiconductor layer 9.

FIGS. 5A-5H illustrate structural changes in a memory opening 49, whichis one of the memory openings 49 in the exemplary structure of FIGS. 4Aand 4B. The same structural change occurs simultaneously in each of theother memory openings 49 and in each support opening 19.

Referring to FIG. 5A, a memory opening 49 in the exemplary devicestructure of FIGS. 4A and 4B is illustrated. The memory opening 49extends through the insulating cap layer 70, the alternating stack (32,42), the gate dielectric layer 12, and optionally into an upper portionof the semiconductor material layer 10. At this processing step, eachsupport opening 19 can extend through the retro-stepped dielectricmaterial portion 65, a subset of layers in the alternating stack (32,42), the gate dielectric layer 12, and optionally through the upperportion of the semiconductor material layer 10. The recess depth of thebottom surface of each memory opening with respect to the top surface ofthe semiconductor material layer 10 can be in a range from 0 nm to 30nm, although greater recess depths can also be employed. Optionally, thesacrificial material layers 42 can be laterally recessed partially toform lateral recesses (not shown), for example, by an isotropic etch.

Referring to FIG. 5B, an optional pedestal channel portion (e.g., anepitaxial pedestal) 11 can be formed at the bottom portion of eachmemory opening 49 and each support openings 19, for example, byselective epitaxy. Each pedestal channel portion 11 comprises a singlecrystalline semiconductor material in epitaxial alignment with thesingle crystalline semiconductor material of the semiconductor materiallayer 10. In one embodiment, the pedestal channel portion 11 can bedoped with electrical dopants of the same conductivity type as thesemiconductor material layer 10. In one embodiment, the top surface ofeach pedestal channel portion 11 can be formed above a horizontal planeincluding the top surface of a sacrificial material layer 42. In thiscase, at least one source select gate electrode can be subsequentlyformed by replacing each sacrificial material layer 42 located below thehorizontal plane including the top surfaces of the pedestal channelportions 11 with a respective conductive material layer. The pedestalchannel portion 11 can be a portion of a transistor channel that extendsbetween a source region to be subsequently formed in the substrate (9,10) and a drain region to be subsequently formed in an upper portion ofthe memory opening 49. A memory cavity 49′ is present in the unfilledportion of the memory opening 49 above the pedestal channel portion 11.In one embodiment, the pedestal channel portion 11 can comprise singlecrystalline silicon. In one embodiment, the pedestal channel portion 11can have a doping of the first conductivity type, which is the same asthe conductivity type of the semiconductor material layer 10 that thepedestal channel portion contacts. If a semiconductor material layer 10is not present, the pedestal channel portion 11 can be formed directlyon the substrate semiconductor layer 9, which can have a doping of thefirst conductivity type.

Referring to FIG. 5C, a stack of layers including a blocking dielectriclayer 52, a charge storage layer 54, a tunneling dielectric layer 56,and an optional first semiconductor channel layer 601 can besequentially deposited in the memory openings 49.

The blocking dielectric layer 52 can include a single dielectricmaterial layer or a stack of a plurality of dielectric material layers.In one embodiment, the blocking dielectric layer can include adielectric metal oxide layer consisting essentially of a dielectricmetal oxide. As used herein, a dielectric metal oxide refers to adielectric material that includes at least one metallic element and atleast oxygen. The dielectric metal oxide may consist essentially of theat least one metallic element and oxygen, or may consist essentially ofthe at least one metallic element, oxygen, and at least one non-metallicelement such as nitrogen. In one embodiment, the blocking dielectriclayer 52 can include a dielectric metal oxide having a dielectricconstant greater than 7.9, i.e., having a dielectric constant greaterthan the dielectric constant of silicon nitride.

Non-limiting examples of dielectric metal oxides include aluminum oxide(Al₂O₃), hafnium oxide (HfO₂), lanthanum oxide (LaO₂), yttrium oxide(Y₂O₃), tantalum oxide (Ta₂O₅), silicates thereof, nitrogen-dopedcompounds thereof, alloys thereof, and stacks thereof. The dielectricmetal oxide layer can be deposited, for example, by chemical vapordeposition (CVD), atomic layer deposition (ALD), pulsed laser deposition(PLD), liquid source misted chemical deposition, or a combinationthereof. The thickness of the dielectric metal oxide layer can be in arange from 1 nm to 20 nm, although lesser and greater thicknesses canalso be employed. The dielectric metal oxide layer can subsequentlyfunction as a dielectric material portion that blocks leakage of storedelectrical charges to control gate electrodes. In one embodiment, theblocking dielectric layer 52 includes aluminum oxide. In one embodiment,the blocking dielectric layer 52 can include multiple dielectric metaloxide layers having different material compositions.

Alternatively or additionally, the blocking dielectric layer 52 caninclude a dielectric semiconductor compound such as silicon oxide,silicon oxynitride, silicon nitride, or a combination thereof. In oneembodiment, the blocking dielectric layer 52 can include silicon oxide.In this case, the dielectric semiconductor compound of the blockingdielectric layer 52 can be formed by a conformal deposition method suchas low pressure chemical vapor deposition, atomic layer deposition, or acombination thereof. The thickness of the dielectric semiconductorcompound can be in a range from 1 nm to 20 nm, although lesser andgreater thicknesses can also be employed. Alternatively, the blockingdielectric layer 52 can be omitted, and a backside blocking dielectriclayer can be formed after formation of backside recesses on surfaces ofmemory films to be subsequently formed.

Subsequently, the charge storage layer 54 can be formed. In oneembodiment, the charge storage layer 54 can be a continuous layer orpatterned discrete portions of a charge trapping material including adielectric charge trapping material, which can be, for example, siliconnitride. Alternatively, the charge storage layer 54 can include acontinuous layer or patterned discrete portions of a conductive materialsuch as doped polysilicon or a metallic material that is patterned intomultiple electrically isolated portions (e.g., floating gates), forexample, by being formed within lateral recesses into sacrificialmaterial layers 42. In one embodiment, the charge storage layer 54includes a silicon nitride layer. In one embodiment, the sacrificialmaterial layers 42 and the insulating layers 32 can have verticallycoincident sidewalls, and the charge storage layer 54 can be formed as asingle continuous layer.

In another embodiment, the sacrificial material layers 42 can belaterally recessed with respect to the sidewalls of the insulatinglayers 32, and a combination of a deposition process and an anisotropicetch process can be employed to form the charge storage layer 54 as aplurality of memory material portions that are vertically spaced apart.While the present disclosure is described employing an embodiment inwhich the charge storage layer 54 is a single continuous layer,embodiments are expressly contemplated herein in which the chargestorage layer 54 is replaced with a plurality of memory materialportions (which can be charge trapping material portions or electricallyisolated conductive material portions) that are vertically spaced apart.

The charge storage layer 54 can be formed as a single charge storagelayer of homogeneous composition, or can include a stack of multiplecharge storage layers. The multiple charge storage layers, if employed,can comprise a plurality of spaced-apart floating gate material layersthat contain conductive materials (e.g., metal such as tungsten,molybdenum, tantalum, titanium, platinum, ruthenium, and alloys thereof,or a metal silicide such as tungsten silicide, molybdenum silicide,tantalum silicide, titanium silicide, nickel silicide, cobalt silicide,or a combination thereof) and/or semiconductor materials (e.g.,polycrystalline or amorphous semiconductor material including at leastone elemental semiconductor element or at least one compoundsemiconductor material). Alternatively or additionally, the chargestorage layer 54 may comprise an insulating charge trapping material,such as one or more silicon nitride segments. Alternatively, the chargestorage layer 54 may comprise conductive nanoparticles such as metalnanoparticles, which can be, for example, ruthenium nanoparticles. Thecharge storage layer 54 can be formed, for example, by chemical vapordeposition (CVD), atomic layer deposition (ALD), physical vapordeposition (PVD), or any suitable deposition technique for storingelectrical charges therein. The thickness of the charge storage layer 54can be in a range from 2 nm to 20 nm, although lesser and greaterthicknesses can also be employed.

The tunneling dielectric layer 56 includes a dielectric material throughwhich charge tunneling can be performed under suitable electrical biasconditions. The charge tunneling may be performed through hot-carrierinjection or by Fowler-Nordheim tunneling induced charge transferdepending on the mode of operation of the monolithic three-dimensionalNAND string memory device to be formed. The tunneling dielectric layer56 can include silicon oxide, silicon nitride, silicon oxynitride,dielectric metal oxides (such as aluminum oxide and hafnium oxide),dielectric metal oxynitride, dielectric metal silicates, alloys thereof,and/or combinations thereof. In one embodiment, the tunneling dielectriclayer 56 can include a stack of a first silicon oxide layer, a siliconoxynitride layer, and a second silicon oxide layer, which is commonlyknown as an ONO stack. In one embodiment, the tunneling dielectric layer56 can include a silicon oxide layer that is substantially free ofcarbon or a silicon oxynitride layer that is substantially free ofcarbon. The thickness of the tunneling dielectric layer 56 can be in arange from 2 nm to 20 nm, although lesser and greater thicknesses canalso be employed.

The optional first semiconductor channel layer 601 includes asemiconductor material such as at least one elemental semiconductormaterial, at least one III-V compound semiconductor material, at leastone II-VI compound semiconductor material, at least one organicsemiconductor material, or other semiconductor materials known in theart. In one embodiment, the first semiconductor channel layer 601includes amorphous silicon or polysilicon. The first semiconductorchannel layer 601 can be formed by a conformal deposition method such aslow pressure chemical vapor deposition (LPCVD). The thickness of thefirst semiconductor channel layer 601 can be in a range from 2 nm to 10nm, although lesser and greater thicknesses can also be employed. Amemory cavity 49′ is formed in the volume of each memory opening 49 thatis not filled with the deposited material layers (52, 54, 56, 601).

Referring to FIG. 5D, the optional first semiconductor channel layer601, the tunneling dielectric layer 56, the charge storage layer 54, theblocking dielectric layer 52 are sequentially anisotropically etchedemploying at least one anisotropic etch process. The portions of thefirst semiconductor channel layer 601, the tunneling dielectric layer56, the charge storage layer 54, and the blocking dielectric layer 52located above the top surface of the insulating cap layer 70 can beremoved by the at least one anisotropic etch process. Further, thehorizontal portions of the first semiconductor channel layer 601, thetunneling dielectric layer 56, the charge storage layer 54, and theblocking dielectric layer 52 at a bottom of each memory cavity 49′ canbe removed to form openings in remaining portions thereof. Each of thefirst semiconductor channel layer 601, the tunneling dielectric layer56, the charge storage layer 54, and the blocking dielectric layer 52can be etched by a respective anisotropic etch process employing arespective etch chemistry, which may, or may not, be the same for thevarious material layers.

Each remaining portion of the first semiconductor channel layer 601 canhave a tubular configuration. The charge storage layer 54 can comprise acharge trapping material or a floating gate material. In one embodiment,each charge storage layer 54 can include a vertical stack of chargestorage regions that store electrical charges upon programming. In oneembodiment, the charge storage layer 54 can be a charge storage layer inwhich each portion adjacent to the sacrificial material layers 42constitutes a charge storage region.

A surface of the pedestal channel portion 11 (or a surface of thesemiconductor material layer 10 in case the pedestal channel portions 11are not employed) can be physically exposed underneath the openingthrough the first semiconductor channel layer 601, the tunnelingdielectric layer 56, the charge storage layer 54, and the blockingdielectric layer 52. Optionally, the physically exposed semiconductorsurface at the bottom of each memory cavity 49′ can be verticallyrecessed so that the recessed semiconductor surface underneath thememory cavity 49′ is vertically offset from the topmost surface of thepedestal channel portion 11 (or of the semiconductor substrate layer 10in case pedestal channel portions 11 are not employed) by a recessdistance. A tunneling dielectric layer 56 is located over the chargestorage layer 54. A set of a blocking dielectric layer 52, a chargestorage layer 54, and a tunneling dielectric layer 56 in a memoryopening 49 constitutes a memory film 50, which includes a plurality ofcharge storage regions (as embodied as the charge storage layer 54) thatare insulated from surrounding materials by the blocking dielectriclayer 52 and the tunneling dielectric layer 56. In one embodiment, thefirst semiconductor channel layer 601, the tunneling dielectric layer56, the charge storage layer 54, and the blocking dielectric layer 52can have vertically coincident sidewalls.

Referring to FIG. 5E, a second semiconductor channel layer 602 can bedeposited directly on the semiconductor surface of the pedestal channelportion 11 or the semiconductor substrate layer 10 if the pedestalchannel portion 11 is omitted, and directly on the first semiconductorchannel layer 601. The second semiconductor channel layer 602 includes asemiconductor material such as at least one elemental semiconductormaterial, at least one III-V compound semiconductor material, at leastone II-VI compound semiconductor material, at least one organicsemiconductor material, or other semiconductor materials known in theart. In one embodiment, the second semiconductor channel layer 602includes amorphous silicon or polysilicon. The second semiconductorchannel layer 602 can be formed by a conformal deposition method such aslow pressure chemical vapor deposition (LPCVD). The thickness of thesecond semiconductor channel layer 602 can be selected to completelyfill remaining volumes of the cavities 49′. The second semiconductorchannel layer 602 may fully fill the cavity 49′ in each memory opening49.

Referring to FIG. 5F, the horizontal portion of the second semiconductorchannel layer 602 can be removed from above the horizontal planeincluding the top surface of the insulating cap layer 70 by aplanarization process. For example, a recess etch or chemical mechanicalplanarization can be employed to remove the horizontal portion of thesecond semiconductor channel layer 602. Each remaining portion of thesecond semiconductor channel layer 602 can be located entirety within amemory opening 49 or entirely within a support opening 19.

Each adjoining pair of a first semiconductor channel layer 601 and asecond semiconductor channel layer 602 can collectively form a verticalsemiconductor channel 60 through which electrical current can flow whena vertical NAND device including the vertical semiconductor channel 60is turned on. A tunneling dielectric layer 56 is surrounded by a chargestorage layer 54, and laterally surrounds a portion of the verticalsemiconductor channel 60. Each adjoining set of a blocking dielectriclayer 52, a charge storage layer 54, and a tunneling dielectric layer 56collectively constitute a memory film 50, which can store electricalcharges with a macroscopic retention time. In some embodiments, ablocking dielectric layer 52 may not be present in the memory film 50 atthis step, and a blocking dielectric layer may be subsequently formedafter formation of backside recesses. As used herein, a macroscopicretention time refers to a retention time suitable for operation of amemory device as a permanent memory device such as a retention time inexcess of 24 hours.

Referring to FIG. 5G, drain regions 63 can be formed by implantingdopants of a second conductivity type that is the opposite of the firstconductivity type. For example, if the first conductivity type isp-type, the second conductivity type is n-type, and vice versa. Thedopant concentration in the drain regions 63 can be in a range from5.0×10¹⁹/cm³ to 2.0×10²¹/cm³, although lesser and greater dopantconcentrations can also be employed. In one embodiment, thesemiconductor material layer 10, the pedestal channel portions 11, andthe vertical semiconductor channels 60 can have a doping of the firstconductivity type (such as p-type), and the drain regions 63 can have adoping of the second conductivity type (such as n-type).

FIG. 5H illustrates an alternative structure according to an alternativeembodiment. In this embodiment, in case the memory cavity 49′ shown inFIG. 5D in each memory opening is not completely filled by the secondsemiconductor channel layer 602, a dielectric core layer can bedeposited in the memory cavity 49′ to fill any remaining portion of thememory cavity 49′ within each memory opening. The dielectric core layerincludes a dielectric material such as silicon oxide or organosilicateglass. The dielectric core layer can be deposited by a conformaldeposition method such as low pressure chemical vapor deposition(LPCVD), or by a self-planarizing deposition process such as spincoating.

The horizontal portion of the dielectric core layer can be removed, forexample, by a recess etch from above the top surface of the insulatingcap layer 70. Each remaining portion of the dielectric core layerconstitutes a dielectric core 62. Further, the horizontal portion of thesecond semiconductor channel layer 602 located above the top surface ofthe insulating cap layer 70 can be removed by a planarization process,which can employ a recess etch or chemical mechanical planarization(CMP). Each remaining portion of the second semiconductor channel layer602 can be located entirety within a memory opening 49 or entirelywithin a support opening 19.

Referring to FIG. 5H, the top surface of each dielectric core 62 can befurther recessed within each memory opening, for example, by a recessetch to a depth that is located, for example, between the top and bottomsurfaces of the insulating cap layer 70 (e.g., at or below the bottomsurface drain side select gate level). Channel extension regions 64 canbe formed by depositing a doped or undoped semiconductor material, suchas amorphous silicon or polysilicon to fill each recessed region abovethe dielectric cores 62. Excess portions of the deposited semiconductormaterial can be removed from above the top surface of the insulating caplayer 70, for example, by chemical mechanical planarization (CMP) or arecess etch to form the channel extension regions 64. If desired, thedrain regions 63 can be implanted into the upper parts of the channelextension regions 64 at this time or at a later stage of the processdescribed below.

Each combination of a memory film 50 and a vertical semiconductorchannel 60 (which is a vertical semiconductor channel) within a memoryopening 49 in the embodiments of FIG. 5G or 5H constitutes a memorystack structure 55. The vertical semiconductor channel 60 may includethe semiconductor channel layers (601 and/or 602) and the optionalchannel extension region 64 shown in FIG. 5H. The memory stack structure55 is a combination of a semiconductor channel, a tunneling dielectriclayer, a plurality of memory elements as embodied as portions of thecharge storage layer 54, and an optional blocking dielectric layer 52.Each combination of a pedestal channel portion 11 (if present), a memorystack structure 55, a dielectric core 62 (if present) and a drain region63 within a memory opening 49 is herein referred to as a memory openingfill structure (11, 55, 63). Each combination of a pedestal channelportion 11 (if present), a memory film 50, a vertical semiconductorchannel 60, a dielectric core 62 (if present) and a drain region 63within each support opening 19 fills the respective support openings 19,and constitutes a support pillar structure 20. A drain region 63 isformed on each of the memory stack structures 55. Each drain regioncontacts a respective memory film 50. Each vertical semiconductorchannel 60 contacts a bottom surface of a respective drain region 63.

Referring to FIGS. 6A and 6B, the exemplary structure is illustratedafter formation of memory opening fill structures (11, 55, 63) andsupport pillar structure 20 within the memory openings 49 and thesupport openings 19, respectively, according to the embodiments of FIG.5G or 5H. While the dielectric core 62 and the channel extension region64 of the embodiment of FIG. 5H is not shown in FIG. 6A, it should beunderstood that they can be included in the structure shown in FIG. 6Aand all of the subsequent figures of the present disclosure. An instanceof a memory opening fill structure (11, 55, 63) can be formed withineach memory opening 49 of the structure of FIGS. 4A and 4B. An instanceof the support pillar structure 20 can be formed within each supportopening 19 of the structure of FIGS. 4A and 4B.

Each memory stack structure 55 includes a memory film 50 and a verticalsemiconductor channel 60, which may comprise multiple semiconductorchannel layers (601, 602) and optionally the channel extension region46. The vertical semiconductor channel 60 is laterally surrounded by thememory film 50. The memory stack structure 55 can be arranged in rowsthat laterally extend along a first horizontal direction hd1. The rowsof memory stack structures 55 can be laterally spaced among one anotheralong a second horizontal direction hd2 that is perpendicular to thefirst horizontal direction hd1. The memory film 50 may comprise atunneling dielectric layer 56 laterally surrounding the verticalsemiconductor channel 60 and a vertical stack of charge storage regionslaterally surrounding the tunneling dielectric layer 56 (as embodied asa memory material layer 54) and an optional blocking dielectric layer52. While the present disclosure is described employing the illustratedconfiguration for the memory stack structure, the methods of the presentdisclosure can be applied to alternative memory stack structuresincluding different layer stacks or structures for the memory film 50and/or for the vertical semiconductor channel 60.

Referring to FIGS. 7A and 7B, a photoresist layer 173 is applied overthe exemplary structure, and is lithographically patterned to formelongated openings that extend along the direction of rows of the memorystack structures 55. Each elongated opening in the patterned photoresistlayer 173 can laterally extend along the first horizontal direction hd1,and can have a uniform width along the second horizontal direction hd2.The width of each elongated opening and the location of each elongatedopening can be selected such that each elongated opening straddles apair of neighboring rows of memory stack structures 55. For each pair ofrows of memory stack structures 55 straddled by an elongated opening, afirst sidewall of the elongated opening that extends along the firsthorizontal direction hd1 can overlie each memory stack structure 55 in afirst row of the pair of rows of memory stack structures 55, and asecond sidewall of the elongated opening that extends along the firsthorizontal direction hd1 can overlie each memory stack structure 55 in asecond row of the pair of rows of memory stack structures 55. In oneembodiment, the fraction of the area of each memory stack structure 55that overlaps with the area of an overlying elongated opening in thephotoresist layer 173 (relative to the total area of the memory stackstructure 55) can be in a range from 0.25 to 0.75, such as from 0.4 to0.6, although lesser and greater fractions can also be employed.

Referring to FIGS. 8A-8C, an anisotropic etch is performed to transferthe pattern of the photoresist layer 173 into underlying materialportions. Specifically, the pattern in the photoresist layer 173 istransferred through the upper portion of the insulating cap layer 70,portions of the drain regions 63, portions of the memory films 50, andportions of the vertical semiconductor channels 60 that are locatedwithin the area of the elongated openings in the photoresist layer 173.If the channel extension regions 64 shown in FIG. 5H are present as thetop parts of the vertical semiconductor channels 60, then the pattern isalso transferred through the channel extension regions 64. A line trench175 is formed underneath each elongated opening in the photoresist layer173 by the anisotropic etch process. The chemistry of the anisotropicetch is non-selective to the materials of the insulating cap layer 70,the drain regions 63, the memory films 50, and the verticalsemiconductor channels 60. Additionally or alternatively, multiple etchchemistries can be employed to etch the various materials of theinsulating cap layer 70, the drain regions 63, the memory films 50, andthe vertical semiconductor channels 60 during the anisotropic etchprocess such that the bottom surface of each line trench 175 can providea substantially flat surface.

Each line trench 175 straddles a neighboring pair of rows of the memorystack structures 55 and extends along the first horizontal directionhd1. Sidewalls of each line trench 175 comprise a sidewall of eachmemory stack structure 55 within the neighboring pair of rows of thememory stack structures 55 (e.g., sidewall of the vertical semiconductorchannel 60, such as a sidewall of the channel extension region 64 of thevertical semiconductor channel 60). Each line trench 175 can be formedby vertically recessing a region of the insulating cap layer 70 and anupper portion of each memory stack structure 55 within the neighboringpair of rows of the memory stack structures 55 by the anisotropic etchprocess. As shown in FIG. 8C, the duration and chemistry of theanisotropic etch process can be selected such that a bottom surface ofeach line trench 175 is formed above a first horizontal plane HP1including a bottom surface of the insulating cap layer 70. A continuousrecessed surface of the insulating cap layer 70 that extend along thefirst horizontal direction is physically exposed at the bottom of eachline trench 175.

Referring to FIGS. 9A-9C, electrical dopants can be implanted into thesidewalls and the bottom surface of the line trenches 175. The implantedportions of the vertical semiconductor channels 60 (e.g., into thechannel extension regions 64 if present) constitute L-shaped dopedregions 612 having a doping of the opposite conductivity type from theconductivity type of the drain regions 63. Specifically, an angled ionimplantation process can be performed to implant dopants of the firstconductivity type into surfaces portions of the vertical semiconductorchannels 60 that underlie physically exposed sidewalls and physicallyexposed recessed horizontal surfaces around the line trenches 175. Eachimplanted region of the vertical semiconductor channels 60 includes avertical portion located directly outside a sidewall of a line trench175, and a horizontal portion located directly underneath a bottomsurface of the line trench 175 that is connected to the vertical portionof the implanted region. As such, the implanted regions of the verticalsemiconductor channel 60 are herein referred to as L-shaped dopedregions 612.

In one embodiment, the first and/or second semiconductor channel layers(601, 602) and optionally the channel extension regions 64 (if present)can have a doping of the first conductivity type at a dopantconcentration in a range from 1.0×10¹⁴/cm³ to 3.0×10¹⁷/cm³, and theL-shaped doped regions 612 can have a heavier (i.e., greater) doping ofthe first conductivity type at a dopant concentration in a range from1.0×10¹⁷/cm³ to 3.0×10¹⁸/cm³, although lesser and greater dopantconcentrations can also be employed. The angle of the ion implantationsteps (as measured from the vertical direction) can be less than 45degrees. In this case, as shown in FIG. 9C, the width w of the verticalportions of the L-shaped doped regions 612 can be less than thethickness t of the horizontal portions of the L-shaped doped regions612, for example, by a factor in a range from 1.1 to 10. The L-shapeddoped regions 612 functions as a conduit for conducting electricalcurrent while the vertical semiconductor channel 60 is turned on, anddrain select gate electrodes to be subsequently formed in the linetrenches can effectively control the current flow through the upperportion of the vertical semiconductor channels located at the level ofthe insulating cap layer 70.

Drain select gate dielectrics can be formed on the physically exposedsurfaces of the vertical semiconductor channels 60 by conversion ofsurface portions of the vertical semiconductor channels 60 intodielectric material portions and/or by deposition of at least onedielectric material layer. As used herein, a “drain select gatedielectric” refers to a gate dielectric for a drain select gateelectrode, i.e., a gate electrode that controls selection of activatedsemiconductor channels from the drain side. Conversion of surfaceportions of the vertical semiconductor channels 60 into dielectricmaterial portions can be effected by thermal oxidation, plasmaoxidation, thermal nitridation, plasma nitridation, or a combinationthereof. The at least one dielectric material layer can include siliconoxide, silicon nitride, silicon oxynitride and/or at least onedielectric metal oxide. FIG. 10 illustrates an embodiment in which acontinuous gate dielectric layer 150L is formed by a conformaldeposition method to provide the drain select gate dielectrics. Forexample, the continuous gate dielectric layer 150L can include a siliconoxide layer having a thickness in a range from 2 nm to 6 nm, althoughlesser and greater thicknesses can also be employed.

Referring to FIGS. 11A-11C, at least one conductive material can bedeposited on the continuous gate dielectric layer 150L (or on discretedrain select gate dielectrics in case the drain select gate dielectricsare formed as discrete dielectric material portions) by a conformaldeposition (such as chemical vapor deposition or electroplating) or by anon-conformal deposition (such as physical vapor deposition). Forexample, the at least one conductive material can include a conductivemetallic nitride liner including TiN, TaN, and/or WN, and a conductivefill material layer such as tungsten, copper, aluminum, and/or cobalt.The thickness of the conductive fill material layer is selected suchthat entire width, such as entire volume, of the line trenches 175 isfilled with the drain select gate dielectrics and the at least oneconductive material.

Any portions of the at least one conductive material overlying thehorizontal plane including the top surface of the insulating cap layer70 are removed by a planarization process, which can include chemicalmechanical planarization and/or a recess etch. Further, the at least oneconductive material can be further recessed below the horizontal planeincluding the top surface of the insulating cap layer 70 by a recessetch, which can employ an isotropic etch or an anisotropic etch. Eachremaining portion of the at least one conductive material in the linetrenches 175 constitutes a drain select electrode line 152, which is adrain select gate electrode that controls flow of electrical currentthrough the upper portion of the vertical semiconductor channels 60(e.g., the channel extension region 64 if present) located at the levelof the insulating cap layer 70 and includes the L-shaped doped regions612. A top surface of the drain select electrode line 152 is formedbelow a second horizontal plane HP2 including the top surface of theinsulating cap layer 70, as shown in FIG. 11C.

In case the drain select gate dielectrics include respective portions ofthe continuous gate dielectric layer 150L, the recess depth may be thesame as the height of the drain regions 63, may be less than the heightof the drain regions 63, or may be greater than the height of the drainregions 63 depending on the duration of the recess etch process.Physically exposed portions of the continuous gate dielectric layer 150Llocated above the horizontal plane including the top surfaces of thedrain select electrode lines 152 may, or may not, be subsequentlyremoved by an isotropic etch (such as a wet etch). In case the exposedportions of the continuous gate dielectric layer 150L located above thehorizontal plane including the top surfaces of the drain selectelectrode lines 152 are removed, top surfaces and sidewalls of the drainregions 63 may be physically exposed. Each remaining portion of thecontinuous gate dielectric layer 150L constitutes a drain select gatedielectric 150.

Alternatively, the drain select gate dielectrics 150 may be formed asdiscrete structures that are self-aligned to the physically exposedsurfaces of the semiconductor channels 60 at the time of formation atthe processing steps of FIG. 10. In this case, the at least oneconductive material is recessed sufficiently, for example, below thehorizontal plane including the bottom surfaces of the drain regions 63,to prevent electrical short between the drain regions 63 and the drainselect electrode lines 152. In an alternative embodiment, the drainregions 63 are formed after recessing the drain select electrode linesby angled ion implantation into the L-shaped doped regions 612 and/orinto the upper portions of the vertical semiconductor channels 60 (e.g.,into the channel extension regions 64, if present).

Generally, a drain select gate dielectric 150 is formed on each L-shapeddoped region 150. The drain select gate dielectric 150 may be acontinuous layer that contacts each L-shaped doped region 612 within apair of rows of memory stack structures 55, or may be discretedielectric material portions that contacts only a respective one of theL-shaped doped regions 150 within a pair of rows of memory stackstructures 55. In one embodiment, a drain select gate dielectric 150 canbe formed on the sidewalls of a line trench 175 and the bottom surfaceof the line trench 175. A drain select electrode line 152 is formed oneach drain select gate dielectric 150 in a line trench 175. Each drainselect electrode line 152 can have a uniform vertical cross-sectionalarea along vertical planes that are perpendicular to the lengthwisedirection of the drain select electrode lines 152, i.e., the firsthorizontal direction hd1. In one embodiment, the uniform verticalcross-sectional area can have the shape of a rectangle or an invertedtrapezoid with a taper angle less than 10 degrees (as measured from thevertical direction).

Referring to FIGS. 12A-12C, a contact level dielectric layer 73including a dielectric material (such as silicon oxide) can be depositedto fill the recessed regions overlying the drain select electrode lines152. FIGS. 12A and 12B illustrate an embodiment in which the topsurfaces of the drain select electrode lines 152 are located above thehorizontal plane including the bottom surfaces of the drain regions 63.FIG. 12C illustrates an embodiment in which the top surfaces of thedrain select electrode lines 152 are located below the horizontal planeincluding the bottom surfaces of the drain regions 63.

The contact level dielectric layer 73 includes a dielectric materialthat is different from the dielectric material of the sacrificialmaterial layers 42. For example, the contact level dielectric layer 73can include silicon oxide. The contact level dielectric layer 73 canhave a thickness in a range from 50 nm to 500 nm, although lesser andgreater thicknesses can also be employed.

In one embodiment, the contact level dielectric layer 73 can be formedon the entire top surface of each drain select electrode line 152. Thecontact level dielectric layer 73 may be formed directly on the topsurface and a sidewall of each of the drain regions 63. The contactlevel dielectric layer 73 can be formed on a top surface of each drainselect gate dielectric 150, which can have a U-shaped verticalcross-sectional profile and contact surfaces of each verticalsemiconductor channel 60 within a line trench 175 and laterally extendalong the first horizontal direction hd1, or may have an L-shapedprofile and contacts only one vertical semiconductor channel 60.

Alternatively, if the drain select gate dielectrics 150 are formed asportions of a continuous drain select gate dielectric layer includinghorizontal portions that overlie the drain regions 63 (such as thecontinuous gate dielectric layer 150L illustrated in FIG. 10 and notsubjected to a subsequent etch process), the contact level dielectriclayer 73 may be spaced from the drain regions 63 by such a continuousdrain select gate dielectric layer. In this case, contact leveldielectric layer 73 can be formed on the top surface of the continuousdrain select gate dielectric layer that includes the drain select gatedielectrics 150 as portions therein.

Referring to FIGS. 13A and 13B, a photoresist layer (not shown) can beapplied over the contact level dielectric layer 73, and islithographically patterned to form openings in areas between clusters ofmemory stack structures 55. The pattern in the photoresist layer can betransferred through the contact level dielectric layer 73, thealternating stack (32, 42) and/or the retro-stepped dielectric materialportion 65 employing an anisotropic etch to form backside trenches 79,which vertically extend from the top surface of the contact leveldielectric layer 73 at least to the top surface of the substrate (9,10), and laterally extend through the memory array region 100 and thecontact region 300. In one embodiment, the backside trenches 79 caninclude a source contact opening in which a source contact via structurecan be subsequently formed. The photoresist layer can be removed, forexample, by ashing.

Referring to FIGS. 14 and 15A, an etchant that selectively etches thesecond material of the sacrificial material layers 42 with respect tothe first material of the insulating layers 32 can be introduced intothe backside trenches 79, for example, employing an etch process. FIG.15A illustrates a region of the exemplary structure of FIG. 14. Backsiderecesses 43 are formed in volumes from which the sacrificial materiallayers 42 are removed. The removal of the second material of thesacrificial material layers 42 can be selective to the first material ofthe insulating layers 32, the material of the retro-stepped dielectricmaterial portion 65, the semiconductor material of the semiconductormaterial layer 10, and the material of the outermost layer of the memoryfilms 50. In one embodiment, the sacrificial material layers 42 caninclude silicon nitride, and the materials of the insulating layers 32and the retro-stepped dielectric material portion 65 can be selectedfrom silicon oxide and dielectric metal oxides.

The etch process that removes the second material selective to the firstmaterial and the outermost layer of the memory films 50 can be a wetetch process employing a wet etch solution, or can be a gas phase (dry)etch process in which the etchant is introduced in a vapor phase intothe backside trenches 79. For example, if the sacrificial materiallayers 42 include silicon nitride, the etch process can be a wet etchprocess in which the exemplary structure is immersed within a wet etchtank including phosphoric acid, which etches silicon nitride selectiveto silicon oxide, silicon, and various other materials employed in theart. The support pillar structure 20, the retro-stepped dielectricmaterial portion 65, and the memory stack structures 55 providestructural support while the backside recesses 43 are present withinvolumes previously occupied by the sacrificial material layers 42.

Each backside recess 43 can be a laterally extending cavity having alateral dimension that is greater than the vertical extent of thecavity. In other words, the lateral dimension of each backside recess 43can be greater than the height of the backside recess 43. A plurality ofbackside recesses 43 can be formed in the volumes from which the secondmaterial of the sacrificial material layers 42 is removed. The memoryopenings in which the memory stack structures 55 are formed are hereinreferred to as front side openings or front side cavities in contrastwith the backside recesses 43. In one embodiment, the memory arrayregion 100 comprises an array of monolithic three-dimensional NANDstrings having a plurality of device levels disposed above the substrate(9, 10). In this case, each backside recess 43 can define a space forreceiving a respective word line of the array of monolithicthree-dimensional NAND strings.

Each of the plurality of backside recesses 43 can extend substantiallyparallel to the top surface of the substrate (9, 10). A backside recess43 can be vertically bounded by a top surface of an underlyinginsulating layer 32 and a bottom surface of an overlying insulatinglayer 32. In one embodiment, each backside recess 43 can have a uniformheight throughout.

Physically exposed surface portions of the optional pedestal channelportions 11 and the semiconductor material layer 10 can be convertedinto dielectric material portions by thermal conversion and/or plasmaconversion of the semiconductor materials into dielectric materials. Forexample, thermal conversion and/or plasma conversion can be employed toconvert a surface portion of each pedestal channel portion 11 into atubular dielectric spacer 116, and to convert each physically exposedsurface portion of the semiconductor material layer 10 into a planardielectric portion 616. In one embodiment, each tubular dielectricspacer 116 can be topologically homeomorphic to a torus, i.e., generallyring-shaped. As used herein, an element is topologically homeomorphic toa torus if the shape of the element can be continuously stretchedwithout destroying a hole or forming a new hole into the shape of atorus. The tubular dielectric spacers 116 include a dielectric materialthat includes the same semiconductor element as the pedestal channelportions 11 and additionally includes at least one non-metallic elementsuch as oxygen and/or nitrogen such that the material of the tubulardielectric spacers 116 is a dielectric material. In one embodiment, thetubular dielectric spacers 116 can include a dielectric oxide, adielectric nitride, or a dielectric oxynitride of the semiconductormaterial of the pedestal channel portions 11. Likewise, each planardielectric portion 616 includes a dielectric material that includes thesame semiconductor element as the semiconductor material layer andadditionally includes at least one non-metallic element such as oxygenand/or nitrogen such that the material of the planar dielectric portions616 is a dielectric material. In one embodiment, the planar dielectricportions 616 can include a dielectric oxide, a dielectric nitride, or adielectric oxynitride of the semiconductor material of the semiconductormaterial layer 10.

Referring to FIG. 15B, a backside blocking dielectric layer 44 can beoptionally formed. The backside blocking dielectric layer 44, ifpresent, comprises a dielectric material that functions as a controlgate dielectric for the control gates to be subsequently formed in thebackside recesses 43. In case the blocking dielectric layer 52 ispresent within each memory opening, the backside blocking dielectriclayer 44 is optional. In case the blocking dielectric layer 52 isomitted, the backside blocking dielectric layer 44 is present.

The backside blocking dielectric layer 44 can be formed in the backsiderecesses 43 and on a sidewall of the backside trench 79. The backsideblocking dielectric layer 44 can be formed directly on horizontalsurfaces of the insulating layers 32 and sidewalls of the memory stackstructures 55 within the backside recesses 43. If the backside blockingdielectric layer 44 is formed, formation of the tubular dielectricspacers 116 and the planar dielectric portion 616 prior to formation ofthe backside blocking dielectric layer 44 is optional. In oneembodiment, the backside blocking dielectric layer 44 can be formed by aconformal deposition process such as atomic layer deposition (ALD). Thebackside blocking dielectric layer 44 can consist essentially ofaluminum oxide. The thickness of the backside blocking dielectric layer44 can be in a range from 1 nm to 15 nm, such as 2 to 6 nm, althoughlesser and greater thicknesses can also be employed.

The dielectric material of the backside blocking dielectric layer 44 canbe a dielectric metal oxide such as aluminum oxide, a dielectric oxideof at least one transition metal element, a dielectric oxide of at leastone Lanthanide element, a dielectric oxide of a combination of aluminum,at least one transition metal element, and/or at least one Lanthanideelement. Alternatively or additionally, the backside blocking dielectriclayer 44 can include a silicon oxide layer. The backside blockingdielectric layer 44 can be deposited by a conformal deposition methodsuch as chemical vapor deposition or atomic layer deposition. Thebackside blocking dielectric layer 44 is formed on the sidewalls of thebackside trenches 79, horizontal surfaces and sidewalls of theinsulating layers 32, the portions of the sidewall surfaces of thememory stack structures 55 that are physically exposed to the backsiderecesses 43, and a top surface of the planar dielectric portion 616. Abackside cavity 79′ is present within the portion of each backsidetrench 79 that is not filled with the backside blocking dielectric layer44.

Referring to FIG. 15C, a metallic barrier layer 46A can be deposited inthe backside recesses 43. The metallic barrier layer 46A includes anelectrically conductive metallic material that can function as adiffusion barrier layer and/or adhesion promotion layer for a metallicfill material to be subsequently deposited. The metallic barrier layer46A can include a conductive metallic nitride material such as TiN, TaN,WN, or a stack thereof, or can include a conductive metallic carbidematerial such as TiC, TaC, WC, or a stack thereof. In one embodiment,the metallic barrier layer 46A can be deposited by a conformaldeposition process such as chemical vapor deposition (CVD) or atomiclayer deposition (ALD). The thickness of the metallic barrier layer 46Acan be in a range from 2 nm to 8 nm, such as from 3 nm to 6 nm, althoughlesser and greater thicknesses can also be employed. In one embodiment,the metallic barrier layer 46A can consist essentially of a conductivemetal nitride such as TiN.

Referring to FIGS. 15D and 16, a metal fill material is deposited in theplurality of backside recesses 43, on the sidewalls of the at least onethe backside trench 79, and over the top surface of the contact leveldielectric layer 73 to form a metallic fill material layer 46B. Themetallic fill material can be deposited by a conformal depositionmethod, which can be, for example, chemical vapor deposition (CVD),atomic layer deposition (ALD), electroless plating, electroplating, or acombination thereof. In one embodiment, the metallic fill material layer46B can consist essentially of at least one elemental metal. The atleast one elemental metal of the metallic fill material layer 46B can beselected, for example, from tungsten, cobalt, ruthenium, titanium, andtantalum. In one embodiment, the metallic fill material layer 46B canconsist essentially of a single elemental metal. In one embodiment, themetallic fill material layer 46B can be deposited employing afluorine-containing precursor gas such as WF₆. In one embodiment, themetallic fill material layer 46B can be a tungsten layer including aresidual level of fluorine atoms as impurities. The metallic fillmaterial layer 46B is spaced from the insulating layers 32 and thememory stack structures 55 by the metallic barrier layer 46A, which is ametallic barrier layer that blocks diffusion of fluorine atomstherethrough.

A plurality of electrically conductive layers 46 can be formed in theplurality of backside recesses 43, and a continuous metallic materiallayer 46L can be formed on the sidewalls of each backside trench 79 andover the contact level dielectric layer 73. Each electrically conductivelayer 46 includes a portion of the metallic barrier layer 46A and aportion of the metallic fill material layer 46B that are located betweena vertically neighboring pair of dielectric material layers, which canbe a pair of insulating layers 32, a bottommost insulating layer and agate dielectric layer 12, or a topmost insulating layer and theinsulating cap layer 70. The continuous metallic material layer 46Lincludes a continuous portion of the metallic barrier layer 46A and acontinuous portion of the metallic fill material layer 46B that arelocated in the backside trenches 79 or above the contact leveldielectric layer 73.

Each sacrificial material layer 42 can be replaced with an electricallyconductive layer 46. A backside cavity 79′ is present in the portion ofeach backside trench 79 that is not filled with the backside blockingdielectric layer 44 and the continuous metallic material layer 46L. Atubular dielectric spacer 116 laterally surrounds a pedestal channelportion 11. A bottommost electrically conductive layer 46 laterallysurrounds each tubular dielectric spacer 116 upon formation of theelectrically conductive layers 46.

Referring to FIG. 17, the deposited metallic material of the continuouselectrically conductive material layer 46L is etched back from thesidewalls of each backside trench 79 and from above the contact leveldielectric layer 73, for example, by an isotropic wet etch, ananisotropic dry etch, or a combination thereof. Each remaining portionof the deposited metallic material in the backside recesses 43constitutes an electrically conductive layer 46. Each electricallyconductive layer 46 can be a conductive line structure. Thus, thesacrificial material layers 42 are replaced with the electricallyconductive layers 46.

Each electrically conductive layer 46 can function as a combination of aplurality of control gate electrodes located at a same level and a wordline electrically interconnecting, i.e., electrically shorting, theplurality of control gate electrodes located at the same level. Theplurality of control gate electrodes within each electrically conductivelayer 46 are the control gate electrodes for the vertical memory devicesincluding the memory stack structures 55. In other words, eachelectrically conductive layer 46 can be a word line that functions as acommon control gate electrode for the plurality of vertical memorydevices.

In one embodiment, the removal of the continuous electrically conductivematerial layer 46L can be selective to the material of the backsideblocking dielectric layer 44. In this case, a horizontal portion of thebackside blocking dielectric layer 44 can be present at the bottom ofeach backside trench 79. The gate dielectric layer 12 can be verticallyspaced from the backside trench 79 by the horizontal portion of thebackside blocking dielectric layer 44.

In another embodiment, the removal of the continuous electricallyconductive material layer 46L may not be selective to the material ofthe backside blocking dielectric layer 44 or, the backside blockingdielectric layer 44 may not be employed. In this case, a top surfaceand/or sidewall surface, of the gate dielectric layer 12 can bephysically exposed at the bottom of the backside trench 79 depending onwhether the gate dielectric layer 12 is not removed or partially removedduring removal of the continuous electrically conductive material layer46L. A backside cavity 79′ is present within each backside trench 79.

Referring to FIGS. 18A and 18B, an insulating material layer can beformed in the at least one backside trench 79 and over the contact leveldielectric layer 73 by a conformal deposition process. Exemplaryconformal deposition processes include, but are not limited to, chemicalvapor deposition and atomic layer deposition. The insulating materiallayer includes an insulating material such as silicon oxide, siliconnitride, a dielectric metal oxide, an organosilicate glass, or acombination thereof. In one embodiment, the insulating material layercan include silicon oxide. The insulating material layer can be formed,for example, by low pressure chemical vapor deposition (LPCVD) or atomiclayer deposition (ALD). The thickness of the insulating material layercan be in a range from 1.5 nm to 60 nm, although lesser and greaterthicknesses can also be employed.

If a backside blocking dielectric layer 44 is present, the insulatingmaterial layer can be formed directly on surfaces of the backsideblocking dielectric layer 44 and directly on the sidewalls of theelectrically conductive layers 46. If a backside blocking dielectriclayer 44 is not employed, the insulating material layer can be formeddirectly on sidewalls of the insulating layers 32 and directly onsidewalls of the electrically conductive layers 46.

An anisotropic etch is performed to remove horizontal portions of theinsulating material layer from above the contact level dielectric layer73 and at the bottom of each backside trench 79. Each remaining portionof the insulating material layer constitutes an insulating spacer 74. Abackside cavity 79′ is present within a volume surrounded by eachinsulating spacer 74.

The anisotropic etch process can continue with, or without, a change inthe etch chemistry to remove portions of the optional backside blockingdielectric layer 44 and the planar dielectric portion 616 that underliesthe opening through the insulating spacer 74. An opening is formedthough the planar dielectric portion 616 underneath each backside cavity79′, thereby vertically extending the backside cavity 79′. A top surfaceof the semiconductor material layer 10 can be physically exposed at thebottom of each backside trench 79. The remaining portion of each planardielectric portion 616 is herein referred to as an annular dielectricportion 616′, which can include a dielectric oxide of the semiconductormaterial of the semiconductor material layer 10, have a uniformthickness, and an opening therethrough.

A source region 61 can be formed at a surface portion of thesemiconductor material layer 10 under each backside cavity 79′ byimplantation of electrical dopants into physically exposed surfaceportions of the semiconductor material layer 10. Each source region 61is formed in a surface portion of the substrate (9, 10) that underlies arespective opening through the insulating spacer 74. Due to the straggleof the implanted dopant atoms during the implantation process andlateral diffusion of the implanted dopant atoms during a subsequentactivation anneal process, each source region 61 can have a lateralextent greater than the lateral extent of the opening through theinsulating spacer 74.

An upper portion of the semiconductor material layer 10 that extendsbetween the source region 61 and the plurality of pedestal channelportions 11 constitutes a horizontal semiconductor channel 59 for aplurality of field effect transistors. The horizontal semiconductorchannel 59 is connected to multiple vertical semiconductor channels 60through respective pedestal channel portions 11. The horizontalsemiconductor channel 59 contacts the source region 61 and the pluralityof pedestal channel portions 11. A bottommost electrically conductivelayer 46 provided upon formation of the electrically conductive layers46 within the alternating stack (32, 46) can comprise a select gateelectrode for the field effect transistors. Each source region 61 isformed in an upper portion of the semiconductor substrate (9, 10).Semiconductor channels (59, 11, 60) extend between each source region 61and a respective set of drain regions 63. The semiconductor channels(59, 11, 60) include the vertical semiconductor channels 60 of thememory stack structures 55.

A backside contact via structure 76 can be formed within each backsidecavity 79′. Each contact via structure 76 can fill a respective cavity79′. The contact via structures 76 can be formed by depositing at leastone conductive material in the remaining unfilled volume (i.e., thebackside cavity 79′) of the backside trench 79. For example, the atleast one conductive material can include a conductive liner 76A and aconductive fill material portion 76B. The conductive liner 76A caninclude a conductive metallic liner such as TiN, TaN, WN, TiC, TaC, WC,an alloy thereof, or a stack thereof. The thickness of the conductiveliner 76A can be in a range from 3 nm to 30 nm, although lesser andgreater thicknesses can also be employed. The conductive fill materialportion 76B can include a metal or a metallic alloy. For example, theconductive fill material portion 76B can include W, Cu, Al, Co, Ru, Ni,an alloy thereof, or a stack thereof.

The at least one conductive material can be planarized employing thecontact level dielectric layer 73 overlying the alternating stack (32,46) as a stopping layer. If chemical mechanical planarization (CMP)process is employed, the contact level dielectric layer 73 can beemployed as a CMP stopping layer. Each remaining continuous portion ofthe at least one conductive material in the backside trenches 79constitutes a backside contact via structure 76.

The backside contact via structure 76 extends through the alternatingstack (32, 46), and contacts a top surface of the source region 61. If abackside blocking dielectric layer 44 is employed, the backside contactvia structure 76 can contact a sidewall of the backside blockingdielectric layer 44.

Referring to FIGS. 19A and 19B, additional contact via structures (88,86, 8P) can be formed through the contact level dielectric layer 73, andoptionally through the retro-stepped dielectric material portion 65. Forexample, drain contact via structures 88 can be formed through thecontact level dielectric layer 73 on each drain region 63. Word linecontact via structures 86 can be formed on the electrically conductivelayers 46 through the contact level dielectric layer 73, and through theretro-stepped dielectric material portion 65. Peripheral device contactvia structures 8P can be formed through the retro-stepped dielectricmaterial portion 65 directly on respective nodes of the peripheraldevices.

According to an aspect of the present disclosure, a three-dimensionalmemory device is provided, which includes: an alternating stack ofinsulating layers 32 and electrically conductive layers 46 located overa substrate (9, 10); an insulating cap layer 70 overlying thealternating stack (32, 46); memory stack structures 55 arranged in rowsthat laterally extend along a first horizontal direction hd1 andextending through each layer of the alternating stack (32, 46) and theinsulating cap layer 70, wherein each of the memory stack structures 55comprises a memory film 50 and a vertical semiconductor channel 60laterally surrounded by the memory film 50; a line trench 175 straddlinga neighboring pair of rows of the memory stack structures 55 andextending along the first horizontal direction hd1, wherein sidewalls ofthe line trench 175 comprise a sidewall of each memory stack structure55 within the neighboring pair of rows of the memory stack structures55; and a drain select electrode line 152 located within the line trench175.

In one embodiment, each vertical semiconductor channel 60 contacts abottom surface of a respective drain region 63; and each drain region 63contacts a respective memory film 50. In one embodiment, thethree-dimensional memory device further comprises a drain select gatedielectric 150 contacting at least one of the sidewalls of the linetrench 175 and a bottom surface of the line trench 175, wherein thedrain select electrode line 152 contacts the drain select gatedielectric 150. In one embodiment, the drain select gate dielectric 150can contact a sidewall and a horizontal surface of each memory stackstructure 55 within the pair of rows of memory stack structures 55, andthe drain select electrode line 152 can be embedded within the drainselect gate dielectric 150.

In one embodiment, the vertical semiconductor channel 60 of each memorystack structure 55 can comprise an L-shaped doped region 612 having adoping of an opposite conductivity type from a conductivity type of thedrain regions 63 and contacting a sidewall and a bottom surface of adrain select gate dielectric 150. In one embodiment, the L-shaped dopedregion 612 can have a greater concentration of electrical dopants thanportions of the vertical semiconductor channels 60 (such as the firstand second vertical semiconductor channels (601, 602)) that extendthrough the alternating stack (32, 46) and having the same conductivitytype as the L-shaped doped region 612.

In one embodiment, the three-dimensional memory device can furthercomprise a contact level dielectric layer 73 that contacts an entire topsurface of the drain select electrode line 152. In one embodiment, thecontact level dielectric layer 73 can contact a top surface and asidewall surface of each of the drain regions 63. In one embodiment, adrain select gate dielectric 150 can contact at least one of thesidewalls of the line trench 175 and a bottom surface of the line trench175. The contact level dielectric layer 73 contacts a top surface of thedrain select gate dielectric 150.

In one embodiment, the drain select gate dielectric contacts each of thedrain regions 63 within the pair of rows of memory stack structures 55.In one embodiment, the contact level dielectric layer 73 contacts asidewall of each of the vertical semiconductor channels 60.

In one embodiment, a bottom surface of the line trench 175 can belocated above a first horizontal plane HP1 including a bottom surface ofthe insulating cap layer 70, and a top surface of the drain selectelectrode line 152 is located below a second horizontal plane HP2including a top surface of the insulating cap layer 70.

In one embodiment, since the line trench 175 cuts into the upper part ofeach memory stack structure 55, each of the memory stack structures 55has a circular horizontal cross sectional shape below the bottom surfaceof the line trench 175 (i.e., below the drain select electrode line152). Furthermore, each of the memory stack structures 55 has asemi-circular horizontal cross sectional shape above the bottom surfaceof the line trench 175 (i.e., at and/or above the drain select electrodeline 152). As used herein, a horizontal cross section is a cross sectionlocated in a plane which is parallel to the top surface 7 of thesubstrate 9.

A non-limiting advantage of the structure of the present embodiments isthat it provides a more compact drain elect electrode line 152 and usesless chip area, which reduces the chip size and decreases the cost ofthe device.

The exemplary structures can include a three-dimensional memory device.In one embodiment, the three-dimensional memory device comprises amonolithic three-dimensional NAND memory device. The electricallyconductive layers 46 can comprise, or can be electrically connected to,a respective word line of the monolithic three-dimensional NAND memorydevice. The substrate (9, 10) can comprise a silicon substrate. Thevertical NAND memory device can comprise an array of monolithicthree-dimensional NAND strings over the silicon substrate. At least onememory cell (as embodied as a portion of a charge storage layer 54 at alevel of an electrically conductive layer 46) in a first device level ofthe array of monolithic three-dimensional NAND strings can be locatedover another memory cell (as embodied as another portion of the chargestorage layer 54 at a level of another electrically conductive layer 46)in a second device level of the array of monolithic three-dimensionalNAND strings. The silicon substrate can contain an integrated circuitcomprising a driver circuit (as embodied as a subset of the least onesemiconductor device 700) for the memory device located thereon. Theelectrically conductive layers 46 can comprise a plurality of controlgate electrodes having a strip shape extending substantially parallel tothe top surface of the substrate (9, 10), e.g., between a pair ofbackside trenches 79. The plurality of control gate electrodes comprisesat least a first control gate electrode located in a first device leveland a second control gate electrode located in a second device level.The array of monolithic three-dimensional NAND strings can comprise: aplurality of semiconductor channels (59, 11, 60), wherein at least oneend portion 60 of each of the plurality of semiconductor channels (59,11, 60) extends substantially perpendicular to a top surface of thesubstrate (9, 10) and comprising a respective one of the verticalsemiconductor channels 60; and a plurality of charge storage elements(as embodied as portions of the memory films 50, i.e., portions of thecharge storage layer 54). Each charge storage element can be locatedadjacent to a respective one of the plurality of semiconductor channels(59, 11, 60).

Although the foregoing refers to particular preferred embodiments, itwill be understood that the disclosure is not so limited. It will occurto those of ordinary skill in the art that various modifications may bemade to the disclosed embodiments and that such modifications areintended to be within the scope of the disclosure. Compatibility ispresumed among all embodiments that are not alternatives of one another.The word “comprise” or “include” contemplates all embodiments in whichthe word “consist essentially of” or the word “consists of” replaces theword “comprise” or “include,” unless explicitly stated otherwise. Wherean embodiment employing a particular structure and/or configuration isillustrated in the present disclosure, it is understood that the presentdisclosure may be practiced with any other compatible structures and/orconfigurations that are functionally equivalent provided that suchsubstitutions are not explicitly forbidden or otherwise known to beimpossible to one of ordinary skill in the art. All of the publications,patent applications and patents cited herein are incorporated herein byreference in their entirety.

What is claimed is:
 1. A three-dimensional memory device comprising: analternating stack of insulating layers and electrically conductivelayers located over a substrate; an insulating cap layer overlying thealternating stack; memory stack structures arranged in rows thatlaterally extend along a first horizontal direction and extendingthrough each layer of the alternating stack and the insulating caplayer, wherein each of the memory stack structures comprises a memoryfilm and a vertical semiconductor channel laterally surrounded by thememory film; a line trench straddling a neighboring pair of rows of thememory stack structures and extending along the first horizontaldirection, wherein sidewalls of the line trench comprise a sidewall ofeach memory stack structure within the neighboring pair of rows of thememory stack structures; and a drain select electrode line locatedwithin the line trench; wherein: a bottom surface of the line trench islocated above a first horizontal plane including a bottom surface of theinsulating cap layer; and a top surface of the drain select electrodeline is located below a second horizontal plane including a top surfaceof the insulating cap layer.
 2. The three-dimensional memory device ofclaim 1, wherein: each vertical semiconductor channel contacts a bottomsurface of a respective drain region; and each drain region contacts arespective memory film.
 3. The three-dimensional memory device of claim2, further comprising a drain select gate dielectric contacting at leastone of the sidewalls of the line trench and a bottom surface of the linetrench, wherein the drain select electrode line contacts the drainselect gate dielectric.
 4. The three-dimensional memory device of claim3, wherein the vertical semiconductor channel comprises an L-shapeddoped region having a doping of an opposite conductivity type from aconductivity type of the drain regions and contacting a sidewall and abottom surface of the drain select gate dielectric.
 5. Thethree-dimensional memory device of claim 4, wherein the L-shaped dopedregion has a greater concentration of electrical dopants than portionsof the vertical semiconductor channels that extend through thealternating stack and having a same conductivity type as the L-shapeddoped region.
 6. The three-dimensional memory device of claim 3, furthercomprising a contact level dielectric layer that contacts an entire topsurface of the drain select electrode line.
 7. The three-dimensionalmemory device of claim 6, wherein the contact level dielectric layercontacts a top surface and a sidewall surface of each of the drainregions, and wherein the contact level dielectric layer contacts a topsurface of the drain select gate dielectric.
 8. The three-dimensionalmemory device of claim 6, wherein the drain select gate dielectriccontacts each of the drain regions.
 9. The three-dimensional memorydevice of claim 6, wherein the contact level dielectric layer contacts asidewall of each of the vertical semiconductor channels.
 10. Thethree-dimensional memory device of claim 1, wherein: each of the memorystack structures has a circular horizontal cross sectional shape belowthe bottom surface of the line trench; and each of the memory stackstructures has a semi-circular horizontal cross sectional shape abovethe bottom surface of the line trench.
 11. The three-dimensional memorydevice of claim 1, wherein: the three-dimensional memory devicecomprises a monolithic three-dimensional NAND memory device; theelectrically conductive layers comprise, or are electrically connectedto, a respective word line of the monolithic three-dimensional NANDmemory device; the substrate comprises a silicon substrate; themonolithic three-dimensional NAND memory device comprises an array ofmonolithic three-dimensional NAND strings over the silicon substrate; atleast one memory cell in a first device level of the array of monolithicthree-dimensional NAND strings is located over another memory cell in asecond device level of the array of monolithic three-dimensional NANDstrings; the silicon substrate contains an integrated circuit comprisinga driver circuit for the memory device located thereon; the array ofmonolithic three-dimensional NAND strings comprises: a plurality ofsemiconductor channels, wherein at least one end portion of each of theplurality of semiconductor channels extends substantially perpendicularto a top surface of the substrate and comprises a respective one of thevertical semiconductor channels, and a plurality of charge storageelements embodied as portions of the memory films, each charge storageelement located adjacent to a respective one of the plurality ofsemiconductor channels.
 12. A three-dimensional memory devicecomprising: an alternating stack of insulating layers and electricallyconductive layers located over a substrate; an insulating cap layeroverlying the alternating stack; memory stack structures arranged inrows that laterally extend along a first horizontal direction andextending through each layer of the alternating stack and the insulatingcap layer, wherein each of the memory stack structures comprises amemory film and a vertical semiconductor channel laterally surrounded bythe memory film; a line trench straddling a neighboring pair of rows ofthe memory stack structures and extending along the first horizontaldirection, wherein sidewalls of the line trench comprise a sidewall ofeach memory stack structure within the neighboring pair of rows of thememory stack structures; and a drain select electrode line locatedwithin the line trench; wherein: each vertical semiconductor channelcontacts a bottom surface of a respective drain region; each drainregion contacts a respective memory film; a drain select gate dielectriccontacting at least one of the sidewalls of the line trench and a bottomsurface of the line trench, wherein the drain select electrode linecontacts the drain select gate dielectric; and the verticalsemiconductor channel comprises an L-shaped doped region having a dopingof an opposite conductivity type from a conductivity type of the drainregions and contacting a sidewall and a bottom surface of the drainselect gate dielectric.